High-end digital camera modules, and specifically cellphone (e.g. smartphone) digital cameras include mechanisms that enable advanced optical function such as focus or optical image stabilization (OIS). Such mechanisms may actuate (e.g. displace, shift or tilt) an optical element (e.g. lens, image sensor, mirror) to create the desired optical function. A commonly used actuator is based on voice coil motor (VCM) technology. In VCM technology, a fixed (or permanent) magnet and a coil are used to create actuation force. The coil is positioned in the vicinity of the magnetic field of the fixed magnet. Upon driving current in the coil, a Lorentz force is created on the coil, an in return an equal counter-force is applied on the magnet. The magnet or the coil is rigidly attached to an optical element to construct an actuated assembly. The actuated assembly is then moved by the magnetic Lorenz force. Henceforth, the term VCM may be used to also refer to “VCM actuator”.
In addition to the magnetic force, a mechanical rail is used to set the course of motion for the optical element. The mechanical rail keeps the motion of the optical element in a desired path, as required by optical needs. A typical mechanical rail is known in the art as “spring-guided rail”, in which a spring or set of springs is used to set the motion direction. A VCM that includes a spring-guided rail is referred to as “spring-guided VCM”. For example, US patent application 20110235196 discloses a lens element being shifted in a linear spring rail to create focus. For example, international patent application PCT/M2016/052179 discloses the incorporation and use of a spring guided VCM in a folded camera structure (FCS). The disclosure teaches a lens element being shifted to create focus and OIS and a light folding element being shifted in a rotational manner to create OIS.
Another typical mechanical rail is known in the art a “ball-guided rail”, see e.g. U.S. Pat. No. 8,810,714. With a ball-guided rail, the optical element is bound to move in the desired direction by set of balls confined in a groove (also referred to as “slit”). A VCM that includes a ball-guided rail is referred to as a “ball-guided VCM”. A ball-guided VCM has several advantages over a spring-guided VCM. These include: (1) lower power consumption, because in a spring-guided VCM the magnetic force has to oppose a spring mechanical force, which does not exist in a ball-guided VCM, and (2) higher reliability in drops which may occur during the life-cycle of a camera that includes the VCM.
While the actuation method showed in U.S. Pat. No. 8,810,714 allows linear motion only, in some cases there is a need to create angular motion as well, for example to rotate (tilt) a light folding element (mirror or prism) in order to create OIS as described in PCT/M2016/052179. Therefore there is a need for, and it would be advantages to have, a rotational ball-guided VCM, i.e. a ball-guided VCM that can cause rotation (tilt) of an optical element.